The present invention relates to an apparatus for epitaxially growing a chemical-compound crystal, in which a plurality of raw-material gases are alternately introduced into a closed chamber of a crystal growing device to grow the crystal and, more particularly, to an apparatus for epitaxially growing a chemical-compound crystal, in which a growing rate of a growing film of the chemical-compound crystal is controlled during crystal growth.
In an epitaxial method for growing a chemical-compound crystal, it is very important to control the growing rate of a growing film of the crystal during crystal growth. Conventionally, in a molecular-beam epitaxial growing method, and a migration enhanced epitaxial growing method, vibration of a reflection high-energy electron diffraction (hereinafter referred to as "RHEED") is used to control the growing rate of the growing film on the order of a monomolecular layer. This is reported in the paper, Jpn. J. Appl. Phys. Vol. 23, No. 9 PPL 657- L659 (1984); T. Sakamoto et al, for example.
In practice, the crystal is grown while rotating a crystal substrate, in order to provide a uniform plane of the crystal film.
When the crystal is grown while rotating the crystal substrate as described above, the direction of the crystal axis and the direction of the high-energy electron beam both change due to the rotation of the crystal substrate. Thus, it is practically impossible to control the thickness of the growing film of the crystal by the RHEED process.
In the existing circumstances, accordingly, the thickness of the growing film of the crystal is controlled by the same conditions as growing conditions which are obtained when the crystal substrate is fixed against rotation. For this reason, it is necessary to regulate or control the amounts of the respective raw-material gases charged into the crystal growing device by crucibles. The temperatures of the crucibles are controlled extremely precisely.
However there are other problems, namely the emission of a high-energy electron beam onto the surface of the growing film gives rise to defects in the crystal. To properly use the electron beam, the interior of the crystal growing device must be maintained at super high vacuum.